1. Field of the Invention
The present invention relates to an automatic transmission system using a torque converter provided with a power take-off (hereinafter referred to as PTO) unit.
2. Description of Related Arts
Generally passenger cars have employed automatic transmission systems of hydraulic type using a torque converter on board. While special motor vehicles used for specific purposes, such as a dump truck and a fire truck, have employed a power take-off unit provided to the transmission system for supplying auxiliary power for the function other than running.
The conventional PTO unit provided to the automatic transmission system using a torque converter is so constructed to take power off the rear stage (behind the turbine) of the torque converter. Another type of the PTO unit that takes power off the front stage (pump) of the torque converter has also been proposed. The latter type is designed to obtain power from driving shafts connected with the torque converter pump through mechanical engagement therewith.
The above described PTO unit taking off power through the torque converter is unlikely to apply excessive load to the engine. However it is likely to lower power transmission efficiency owing to slippage of the torque converter. With the latter type of the PTO unit which takes power off the front stage of the torque converter through engagement therewith, if an engine output in idling is relatively lower than the PTO unit load, it may cause knocking or engine failure. Increasing the output to a high level will result in deteriorating fuel consumption.